The invention generally relates to illumination systems for producing light. The invention particularly relates to an illumination system for producing light and for launching the light into a proximal end of an optical cable of an observation apparatus for endoscopy or microscopy. More specifically, the invention relates to an illumination system of the afore-mentioned kind having a cooling apparatus for removing heat produced by a light source of the illumination system.
A thermal conductive connection is to be understood within the context of the present invention to mean direct thermal contact or indirect thermal contact between the cooling apparatus, i.e. the cooling body, and the light source which (contact) can be used to effectively remove the heat produced by the light source.
An illumination system of this kind is used in endoscopy or microscopy in order to illuminate a region which is to be observed. The illumination system is generally connected by means of an optical cable to an endoscope or a microscope in which the light is guided by means of light guiding optics in the form of optical elements and/or light guides. The illumination system therefore needs to provide a sufficient light output in order to be able to illuminate the region to be observed in optimum fashion. The high light output means that the light source produces a large quantity of heat. This quantity of heat produced by the light source needs to be removed so as not to impair the performance of the light source.
US 2005/0201100 A1 discloses an illumination system which has LED as light source. Arranged between the LED and an optical cable, which is used to route the light to the region which is to be observed, is an optical light guiding element in the form of a lens. The lens is used to launch the light into the optical cable so that losses in intensity at the launch point between the LED and the optical cable are reduced. A first end region of the lens on the side of the lens which faces the LED has a smaller cross-sectional area than a second end region of the lens which faces the optical cable.
In addition, the known illumination system has a cooling apparatus which has a cylindrical cooling body which is at a distance from the LED and which at least partially surrounds the LED and the lens. The heat produced by the LED is removed to the cooling body by the LED holder, by a cooling plate which is arranged on a side of the LED which is remote from the lens, or by a reflector in which the LED is accommodated.
A drawback of this illumination system is that the heat produced by the LED is removed by means of small components, i.e. the LED holder, the cooling plate and the reflector, with which the lens is in direct or indirect thermal contact. The large amount of heat produced by the LED means that these small components heat up, and therefore the lens heats up, to a large extent. As a result, thermal stability of the lens is not assured, which means that its optical properties (refractive index or the like) can change. The impaired operation of the lens can result in a reduction in the light output from the illumination system.
It is also found to be disadvantageous that the cooling body is arranged at a physical distance from the light source. Heat is conducted from the light source to the cooling body via the aforementioned small components, which are bottlenecks for the conduction of heat, so that consequently the quantity of heat produced by the LED is delivered to the cooling body poorly. This inadequate cooling impairs the operation of the illumination system.
Another drawback of the illumination system is its design, in which the LED and the lens are accommodated in the cylindrical cooling body. If the LED needs to be replaced on account of its limited life or the lens needs to be replaced as a result of damage, these repairs are found to be particularly time consuming, since both components are not freely accessible but rather are arranged in the cooling body.